Wellbore composite plug assembly

ABSTRACT

A down hole tool assembly can be installed at a desired location within a subterranean wellbore that is capable of isolating one portion of the wellbore from another, while sealing fluid pressure within the wellbore from at least one direction. The plug assembly can include components constructed of non-metallic material that can be drilled, milled or mechanically broken up more quickly and efficiently than conventional wellbore plugs.

CROSS REFERENCES TO RELATED APPLICATION

Priority of U.S. Provisional Patent Application Ser. No. 61/838,524,filed Jun. 24, 2013, and U.S. Provisional Patent Application Ser. No.61/904,077, filed Nov. 14, 2013, both incorporated herein by reference,is hereby claimed.

STATEMENTS AS TO THE RIGHTS TO THE INVENTION MADE UNDER FEDERALLYSPONSORED RESEARCH AND DEVELOPMENT

None

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention pertains to a down hole assembly such as, but notlimited to, a drillable bridge plug that can be installed at a desiredlocation within a subterranean wellbore. More particularly, a preferredembodiment of the present invention pertains to a bridge plug assemblycapable of sealing fluid pressure within a wellbore from at least onedirection. More particularly still, the present invention pertains to aplug assembly that can be drilled, milled or mechanically broken up moreefficiently than conventional wellbore plugs.

2. Brief Description of the Prior Art

It is frequently desirable to set at least one bridge plug or otheranchoring, sealing device within a wellbore. In some cases, suchassemblies are installed to isolate one portion of a wellbore fromanother, prevent fluid flow from one portion of a wellbore to another,and/or provide a fluid pressure sealing barrier within said wellbore.Such down hole bridge plugs or other anchoring, sealing devices arefrequently set within the bore of a casing or tubing string, and bothgrip and provide a fluid pressure seal against the inner wall of suchpipe; however, it is to be observed that in certain applications suchplugs can also be installed within a section of drilled “open hole”.

Conventional bridge plugs used to isolate a portion of a wellbore fromanother portion of said wellbore typically comprise a sealing system orpacking element incorporated into to the design, an anchoring systemthat grips the inner surface of the surrounding wellbore, as well as anadditional internal force storing mechanisms. With such conventionalplugs, a force is required to energize said packing element and actuatesaid anchoring system. In certain assemblies, such force or load issupplied by pipe weight situated above the plug, or by tensile loadingapplied from the wellbore surface. Such conventional plugs generallymust be continually attached to a pipe string during the setting processin order to receive the force required to actuate said anchor system andenergize said sealing mechanism and to continue to energize such system.

Certain conventional bridge plugs internally store setting forcessupplied by an attached tubular, electrically actuated setting tool orhydraulic setting tool and are made to operate alone without anyattachment to said devices. These conventional tools anchor and sealremotely of the said devices and are capable of storing forcestransmitted by such setting devices to remain anchored and sealing.

Of the conventional bridge plugs that internally store setting forces, aportion are made to be drilled with a bit, hammer or mill drillingdevice to be removed from the wellbore when isolation of a portion ofthe wellbore is no longer desired. These conventional drillable bridgeplugs are typically constructed of either drillable cast iron, aluminum,resin impregnated fiber or a combination. Such plugs generally comprisea mandrel, an upper slip support, upper slips, upper cone, upper elementback up system, packing (sealing) element, lower element back up system,lower cone, lower slips, lower slip support and an enclosed locking ringlocated between the upper cone or upper slip support and the mandrel.

When such a conventional plug is set, the mandrel with the attachedlower slip support and/or lower cone move relative to the upper slipassembly causing the upper and lower slip assemblies, to come togetherand contact the cones. The slip assemblies then are forced to extendradially outward toward the inner surface of a surrounding wellbore.Simultaneously, said packing element, typically located between the slipassemblies, compresses as the slip assemblies and cones come together;the packing member extends radially outward along and around themidpoint of the element toward the inner surface of the surroundingwellbore. Said opposing slip assemblies move toward each other, but oncein contact with the inner surface of the surrounding wellbore said slipassemblies cannot move apart. Thus the slip assemblies lock in place toanchor the tool within the wellbore.

As the above sequence occurs, the mandrel moves through the upper slipsupport and for the upper cone as stated. A split lock ring internal tothe upper slip support and for upper cone allows the mandrel to movethrough it in one direction only. The lock ring typically has smallteeth machined on its inside surface and the mandrel has opposing teethmachined on its outside surface. As a result, said mandrel can move onlyin one direction through the lock ring. When a predetermined totalsetting force has been applied, the mandrel and lock ring engage,storing all of the setting force between the upper and lower cone andfurther anchoring the plug within the wellbore.

Such conventional drillable metallic plugs are generally highly reliablein operation, but are frequently too difficult and time consuming (andthus, too expensive) to drill out, mill up or otherwise mechanicallybreak apart. In certain applications, multiple drillable plugs areinstalled within a single wellbore, thus compounding the time and costof drilling, milling or otherwise removing said plugs. By way ofexample, but not limitation, the use of multiple plugs has become verycommon in both vertical and horizontal wells; frequently, multipledrillable plugs are installed in a single well completion.

Certain conventional plugs include components that are constructed fromnon-metallic materials such as, for example, composite materials. Suchconventional plugs can generally be drilled or milled faster and moreefficiently than plugs that are constructed from metallic components.

Such plugs are general designed exactly or substantially the same asdrillable cast iron plugs, except that composite materials aresubstituted for the mandrel, upper slip support, upper cone, upperelement back up system, lower element back up system, lower cone andlower slip support, or various combinations thereof.

One mechanism that has not been reliably replicated by such conventionalcomposite plug devices is the lock ring system that prevents the mandrelfrom moving and unseating the plug when exposed to certain forces.Without a reliable locking mechanism, these composite plugs rely solelyon the energy of the slips and packing element to store the energyrequire to anchor and seal. The mandrels of such conventional compositeplugs are held only by friction forces and are able to move in relationto the slips and packing element when the plug is exposed to asignificant pressure differential. Movement of such mandrel can cause ajarring effect on the plug, which has the ability to decrease the forcestored in the slips and allow some or all of the setting force todissipate resulting in the failure of the bridge plug to hold pressureand anchor.

Thus there is a need for a composite plug that securely locks in placeafter a setting sequence to store setting energy applied to said plug.Said plug assembly can be at least partially constructed of non-metalliccomponents. When desired, said plug assembly should be capable of beingdrilled, milled or otherwise mechanically broken apart more easily andefficiently than conventional composite plugs, while more securelyanchoring and providing a fluid pressure seal within a wellbore.

SUMMARY OF THE INVENTION

In a preferred embodiment, the present invention comprises a plugassembly for down hole use in wellbores such as, for example, in oil orgas wells penetrating subterranean formations. In a preferredembodiment, certain components of the plug assembly of the presentinvention can be beneficially constructed from at least one materialthat can be relatively easily milled or drilled, such as, for example,composite resin impregnated fiber or other material exhibiting similarqualities and characteristics.

Said plug assembly of the present invention comprises a fully sealingassembly, as well as a single slip assembly located either below orabove the sealing assembly. In operation, the plug assembly of thepresent invention can be attached to a setting tool and conveyed into awell to a desired depth via continuous wire (such as, for example,electric line, slick line or braided line), coiled tubing or jointedpipe.

Once said plug assembly of the present invention is positioned at adesired location, said setting tool can be actuated. Upon actuation ofsaid setting tool, certain outer components of said plug assembly areaxially shifted relative to a central mandrel member of said plugassembly that remains substantially in place.

Concurrent to the movement of the setting tool causing the relativemovement between the central mandrel (with an attached mule shoe cone)and the setting cylinder, incompressible fluid located in a first fluidchamber is displaced through a unidirectional seal assembly into asecond fluid chamber. Once said fluid is displaced into said secondfluid chamber, the unidirectional seal assembly traps the fluid in thesecond chamber thereby preventing any additional mandrel movement.

Concurrent to the action stated above, said setting cylinder forces theupper end of a cup forming sealing element to extend radially outwarduntil contacting the inner surface wall of a surrounding wellbore.Continued movement of said mandrel further compresses said sealingelement into the inner surface of the surrounding wellbore.

Additionally, the upper cone and the mule shoe cone come together,thereby forcing the independent bidirectional slips simultaneouslyradially outward to contact the inner surface of the surroundingwellbore. As setting force continues to a predetermined shearing forceof shear pins, resultant force is distributed into the slip assembly andsealing element. Once a predetermined shear force is reached, said shearpins will break releasing the setting tool from the plug assembly of thepresent invention.

The plug assembly of the present invention can be installed down holewithin a wellbore in order to isolate one portion of a wellbore fromanother, prevent fluid flow from one portion of a wellbore to anotherand provide a fluid pressure sealing barrier within said wellbore.Unlike conventional composite bridge plugs, the plug assembly of thepresent invention locks the mandrel in place by hydraulically storingsetting forces within the plug assembly. Said plug assembly can be atleast partially constructed of non-metallic components, and is capableof being drilled, milled or otherwise mechanically broken apart moreeasily and efficiently than conventional composite bridge plugs.

BRIEF DESCRIPTION OF DRAWINGS/FIGURES

The foregoing summary, as well as any detailed description of thepreferred embodiments, is better understood when read in conjunctionwith the drawings and figures contained herein. For the purpose ofillustrating the invention, the drawings and figures show certainpreferred embodiments. It is understood, however, that the invention isnot limited to the specific methods and devices disclosed in suchdrawings or figures.

FIG. 1 depicts a side sectional view of a preferred embodiment of acomposite plug assembly of the present invention.

FIG. 2 depicts a side sectional detailed view of the highlighted areadepicted in FIG. 1.

FIG. 3 depicts a side sectional view of the plug assembly of the presentinvention during the process of being run in a wellbore.

FIG. 4 depicts a side sectional view of the plug assembly of the presentinvention during the plug setting process.

FIG. 5 depicts a side sectional view of the plug assembly of the presentinvention after it has been installed and set in a wellbore.

FIG. 6 depicts a side perspective view of a unidirectional seal assemblyof the present invention.

FIG. 7 depicts a side sectional view of a unidirectional seal assemblyof the present invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

The present invention comprises a plug assembly for down hole use inwellbores such as, for example, in oil or gas wells that penetratesubterranean formations. In a preferred embodiment, certain componentsof the plug assembly of the present invention can be beneficiallymanufactured from at least one material that can be relatively quicklyand efficiently milled, drilled or otherwise mechanically broken apartsuch as, for example, composite resin impregnated fiber or othermaterial exhibiting similar characteristics.

The plug assembly of the present invention can be installed toselectively isolate one portion of a wellbore from another, to preventfluid flow from one portion of a wellbore to another and/or to provide afluid pressure sealing barrier at a desired location within a wellbore.The plug assembly of the present invention can be beneficially setwithin the internal bore of a string of casing, production tubing orother tubular. However, it is to be observed that in certainapplications or down hole environments, the plug assembly of the presentinvention can also be installed within an “open hole” section of awellbore.

Said plug assembly of the present invention comprises a fluid pressuresealing assembly, as well as a slip assembly having independentlyoperating gripping slip members. Although other relative positioning canbe employed without departing from the scope of the present invention,said slips are typically disposed below said sealing assembly. Moreover,in a preferred embodiment, only a single slip assembly is required toanchor the plug assembly of the present invention within a wellbore,unlike conventional plug assemblies that typically require two or moresets of slip assemblies for this purpose; use of a single slip assemblymakes the plug assembly of the present invention easier to drill, millor otherwise mechanically break apart then conventional multi-slipplugs.

In operation, the plug assembly of the present invention can be attachedto a setting tool and conveyed into a well to a desired depth viacontinuous wire (such as, for example, electric line, slick line orbraided line), continuous or coiled tubing, or jointed pipe. Once saidplug assembly is positioned at a desired location within a wellbore—thatis, the depth at which setting of the plug assembly is desired—saidsetting tool can be actuated in order to anchor said plug assembly inplace and energize said seal assembly of said plug assembly.

Referring to the drawings, FIG. 1 depicts a side sectional view of plugassembly 100 of the present invention. Plug assembly 100 comprisessetting cylinder 20 having central through bore 21, upper cone member 40having central through bore 41, setting ring 30 having central throughbore 31 and lower cone member 50 having central through bore 51; saidcentral through bores are substantially axially aligned.

Elongate inner mandrel 10, having central through bore 11 extendingthrough said inner mandrel 10, is internally received within saidsubstantially aligned central through bores 21, 31, 41 and 51. Putanother way, setting cylinder 20, upper cone member 40, spacer sleeve 30and lower cone member 50 are disposed along the outer surface of saidinner mandrel 10. Lower cone member 50 can have bottom mule shoeconfiguration 90, and is beneficially attached to mandrel 10 using fiberpins 91 that extend through aligned transverse bores in mandrel 10 andlower cone member 50.

Sealing member 60 having central through bore 61 is disposed betweensetting cylinder 20 and upper cone member 40; in a preferred embodiment,said sealing member 60 comprises an elastomeric material that is capableof deforming in response to axial compression forces to extend radiallyoutward and create a fluid pressure seal between plug assembly 100 andan inner surface of a surrounding wellbore (not depicted in FIG. 1).

Similarly, at least one slip assembly 70 is disposed along the outersurface of mandrel 10 between upper cone member 40 and lower cone member50. Said at least one slip assembly 70 comprises a plurality of slipmembers 74 having gripping teeth 71 beneficially disposed along theouter surface of said slip members 74. The gripping teeth 71 of slipmembers 74 individually may be oriented opposite of one another, suchthat the gripping direction of said slip members is opposite from eachother. At least one retaining ring 73 can be disposed around said slipmembers 74; said retaining ring 73 can hold said slip members 74 inplace, but can break or shear when exposed to predetermined forcesimparted by slip members 74 in a radially outward direction.

Still referring to FIG. 1, a first void space or lower chamber 22 isformed between an outer surface of mandrel 10, an inner surface ofcentral through bore 21 of setting cylinder 20, and setting ring 30.O-rings 25 provide a fluid pressure seal between central mandrel 10 andsetting ring 30. Similarly, O-rings 26 provide a fluid pressure sealbetween setting ring 30 and setting cylinder 20.

Similarly, a second void space or upper chamber 23 is formed between anouter surface of mandrel 10 and an inner surface of central through bore21 of setting cylinder 20. A fluid channel 24 extends between lowerchamber 22 and upper chamber 23; a unidirectional seal member 80 isdisposed within said fluid channel 24 between said lower chamber 22 andupper chamber 23. O-rings 27 provide a fluid pressure seal between theouter surface of central mandrel 10 and an inner surface of settingcylinder 20, and prevent fluid entering said second chamber 23 fromflowing between said surfaces.

Still referring to FIG. 1, a ball 5 is either run in place, gravity fedfrom the surface or pumped down a surrounding wellbore to plug assembly100, can seat on upper seating surface 13 of central mandrel 10 to stopfluid flow from the surface direction through bore 11 extending throughsaid inner mandrel 10. In a preferred embodiment, ball 5 can beconstructed from resin impregnated fiber or materials with similarcharacteristics. In the view depicted in FIG. 1, shear pins 14 canextend through aligned transverse bores in central mandrel 10 andsetting cylinder 20; said shear pins 14 can be set to break in responseto a predetermined axial shear force acting on said pins 14.

FIG. 2 depicts a side sectional detailed view of the highlighted areadepicted in FIG. 1. Fluid channel 24 extends between lower first chamber22 and upper second chamber 23. Unidirectional seal member 80 isdisposed within said fluid channel 24 between said chamber 22 andchamber 23. As described in detail below, said unidirectional sealmember 80 allows fluid to flow from chamber 22 into chamber 23. However,said seal member 80 forms a fluid pressure seal that prevents fluid flowin the opposite direction—that is, from chamber 23 into chamber 22. Assuch, it is to be observed that any fluid that flows from lower firstchamber 22 into upper second chamber 23 effectively becomes trappedwithin said chamber 23, and cannot flow in a reverse direction pastunidirectional seal member 80 back into said lower first chamber 22.

FIG. 3 depicts a side sectional view of plug assembly 100 of the presentinvention during the process of being conveyed within wellbore 300having inner wall surface 301. In normal operation, plug assembly 100 ofthe present invention is attached to a conventional wireline settingtool 200 and conveyed into wellbore 300 via continuous wireline to adesired depth; however, as noted above, plug assembly 100 can also beconveyed into a wellbore via continuous or coiled tubing, or jointedpipe. It is to observed that plug assembly 100 is partially rotatedabout its longitudinal axis in FIGS. 3 through 5, compared to the viewdepicted in FIG. 1; as a result, certain components, such as shear pins14, are depicted in FIG. 1 but are not visible in FIGS. 3 through 5.

Wireline setting tools are well known to those having skill in the artand can have many different configurations. As depicted in FIG. 3,wireline setting tool 200 comprises outer sleeve 201 and inner tensionmandrel 202. Further, said wireline setting tool 200 can be connected tomandrel 10 of plug assembly 100 using shear screws 12 that are capableof shearing when exposed to predetermined shear forces. Notwithstandingthe foregoing, it is to be observed that plug assembly 100 of thepresent invention can be set using a conventional plug setting tool wellknown to those having skill in the art.

FIG. 4 depicts a side sectional view of plug assembly 100 of the presentinvention during the plug setting process. Once plug assembly 100 ispositioned at a desired location within a wellbore, setting tool 200 isactuated, causing outer sleeve 201 to be axially shifted relative tomandrel 10. Specifically, outer sleeve 201 of setting tool 200 isaxially shifted toward the distal end of plug assembly 100 (that is,substantially in a direction toward mule shoe 90). However, wirelinetension mandrel 202 (and the attached wireline) prevents downward travelof central mandrel 10; thus, mandrel 10 remains substantially stationaryrelative to outer sleeve 201.

Still referring to FIG. 4, as outer sleeve 201 moves axially toward thedistal end of plug assembly 100, said outer sleeve 201 imparts axialforce on setting cylinder 20 while (as noted above) inner mandrel 10remains substantially stationary relative to setting cylinder 20. Saidsetting cylinder 20, in turn, applies axial forces on sealing member 60,which is axially compressed between setting cylinder 20 and upper conemember 40. Such compressive forces cause said sealing member 60 todeform and extend radially outward, thereby forcing and compressing saidsealing member 60 against inside surface 301 of the surrounding wellbore300.

When a predetermined axial force is met, shear screws 12 that are usedto attach plug assembly 100 to setting tool 200 break, thereby releasingplug assembly 100 from said setting tool 200 from said plug assembly100. Thereafter, said setting tool 200 can be retrieved from thewellbore via wireline (or other means used to convey it in saidwellbore).

FIG. 5 depicts a side sectional view of plug assembly 100 of the presentinvention after it has been installed and set within wellbore 300, andafter setting tool 200 has been removed. As part of the setting processdescribed above, axial forces are conveyed through sealing member 60 toupper cone member 40 which, in turn, acts on slip assembly 70. Asindividual slip members 74 of slip assembly 70 are exposed tocompressive forces between lower cone member 50 and upper cone member40, tapered surfaces 72 of slip members 74 ride on corresponding taperedsurfaces 52 of lower cone member 50, thereby causing said slip members74 to extend radially outward. Such compressive forces drive slipmembers 74 radially outward, breaking any retaining ring(s) 73 (notdepicted in FIG. 5, but visible in FIG. 3) disposed around said slipmembers 74 and forcing gripping teeth 71 of slip members 74 toward innersurface 301 of the surrounding wellbore 300.

Said gripping teeth 71 of slip members 74 can partially embed within theinner surface 301 of surrounding wellbore 300, thereby increasingfrictional forces acting between said plug assembly 100 and saidsurrounding wellbore 300. When deployed radially outward, said slipmembers 74 serve to anchor said plug assembly 100 in place withinwellbore 300 and resist axial displacement of said plug assembly 100within said surrounding wellbore 300, even when said plug assembly 100is exposed to a fluid pressure differential across said plug assembly100. In a preferred embodiment, certain of said slip members 74 andgripping teeth thereof can be oriented bi-directionally, in opposingaxial directions. As such, when engaged against an inner surface of awellbore, certain of said slip members 74 act to resist movement in oneaxial direction (for example, upward within said wellbore), whilecertain other of said slip members 74 act to resist movement in anopposite axial direction (for example, downward within said wellbore).

Still referring to FIG. 5, in a preferred embodiment sealing member 60of the present invention comprises at least one cup-type sealing elementprofile 62, which can be constructed of completely elastomeric materialrequiring no backup sealing system of any kind (such as a metal supportring, composite support ring or elastomer support ring or base). Asfluid pressure is applied to said sealing element 60, such pressureforces said cup-type sealing element profile(s) 62 radially outward tocontact against inner surface 301 of surrounding wellbore 301 (typicallythe inner surface of a casing string) and form a fluid pressure seal.Generally, the greater the pressure, the greater the outward (sealing)force on said cup-type sealing element(s).

When plug assembly 100 will only be exposed to pressure from one axialdirection (such as, for example, so-called “frac plugs” that are exposedto pressure only from above), said plug assembly 100 can beneficiallyemploy a single cup-type sealing element. By contrast, plug assembliesthat are exposed to pressure from opposing axial directions (such as,for example, bridge plugs that must seal from above and below said plug)can have at least two (2) opposing cup-type sealing elements that areoriented in opposite axial directions.

As noted previously, ball 5 is either run in place, gravity fed from thesurface or pumped down a surrounding wellbore to plug assembly 100, canseat on upper seating surface 13 of central mandrel 10 to stop fluidflow from the surface direction through bore 11 extending through saidinner mandrel 10. In a preferred embodiment, ball 5 can be constructedfrom resin impregnated fiber or materials with similar characteristics.

In a preferred embodiment, slip assembly 70 of plug assembly 100 isbeneficially located below said sealing member 60 (that is, betweensealing member 60 and mule shoe 90). As a result, when plug assembly 100of the present invention is milled, drilled or otherwise mechanicallybroken apart (such as, for example, at the end of its useful life) fromthe upper opening of a wellbore, the sealing element(s) of sealingmember 60 can be fully removed (i.e., drilled, milled or otherwisemechanically broken apart), thereby allowing any fluid pressuredifferential across said plug assembly 100 to equalize and becomebalanced across said plug assembly 100 before said slip assembly 70 ismilled/drilled and plug assembly 100 is released from its grip withinwellbore 300. Such pressure equalization will typically result in suchdrilling/milling operation being safer and more efficient.

Referring back to FIG. 2, during the setting sequence described hereinsetting cylinder 20 moves in an axial direction toward the distal end ofplug assembly 100, forcing an incompressible fluid to flow from lowerfirst fluid chamber 22 through fluid channel 24 and unidirectional sealmember 80, and into upper second fluid chamber 23 (the volume of whichincreases due to said relative movement between setting cylinder 20 andcentral mandrel 10). Said unidirectional seal member 80 allows saidincompressible fluid to pass in one direction only; once saidincompressible fluid is in upper second fluid chamber 23, saidunidirectional seal member 80 prevents said fluid from flowing ortransferring back to said lower first chamber 22, thereby hydraulicallystoring such setting forces and locking central mandrel 10 in place.Referring to FIG. 1, it is to be observed the O-rings 27 further preventsuch fluid in upper second fluid chamber 23 from escaping through anygap or channel formed between setting cylinder 20 and inner mandrel 10.

While this setting/locking technology of the present invention isadvantageously used in tools made with composite materials like plugassembly 100 for facilitating drill ability, such setting technology canalso be applied to plug assemblies and other tools constructed of othernon-composite materials (such as, for example, cast iron or steel) whensuch.

FIG. 6 depicts a side perspective view of a unidirectional seal assembly80 of the present invention. Unidirectional fluid pressure seal assembly80 permits fluid to flow through said seal assembly 80 in one direction,while forming a fluid pressure seal or closure when said fluid attemptsto flow through said seal assembly 80 in an opposite or reversedirection. Although other applications can be envisioned withoutdeparting from the scope of the present invention, as discussed hereinsaid seal assembly 80 of the present invention can be beneficially usedto provide a unidirectional fluid pressure seal within an annular spaceformed between cylindrical members (see, for example, FIG. 2 hereof).

Still referring to FIG. 6, seal assembly 80 generally comprisesring-like circular body member 81 defining an inner surface 82 having adiameter. FIG. 7 depicts a side sectional view of said a unidirectionalseal assembly 80 of the present invention. In a preferred embodiment,said seal assembly 80 of the present invention comprises a substantiallycircular ring-like body member 81. One side of body member 81 defines asubstantially “Y” shape having substantially parallel finger members 83and central vertex section 84.

Said “Y”-shape or cup forms a pressure containing side of seal assembly80. Seal assembly 80 of the present invention also contains anon-pressure containing side, or a backside surface 85, that defines asubstantially rectangular surface. A plurality—typically eight (8)—ofcut-outs 86 are formed in non-sealing surface 85 and extend to innersurface 82. In a preferred embodiment, said cut-outs 86 can besubstantially semi-circular or scalloped in shape and equidistantlyspaced around the inner diameter of circular ring-like body member 81 ofseal assembly 80 of the present invention.

In a preferred embodiment, inner surface 82 of the seal member forms aninterference fit with an outer surface of a smaller cylinder that is tobe sealed to the present invention, thereby comprising a match in sizeand shape between the seal and the smaller cylinder. Additionally, saidseal assembly 80 beneficially sits in a pocket or recess formed within alarger diameter cylinder; the outer diameter of seal assembly 80 and theinner diameter of said pocket or recess being substantially equal, suchthat said pocket or recess holds seal assembly 80 of the presentinvention in place.

In a preferred embodiment, by way of illustration, but not limitation,seal assembly 80 can be manufactured from Hydrogenated Nitrile ButadieneRubber (HNBR) with a 90 Duro A Shore Hardness; however, other types ofmaterials or elastomers may be used. Dimensions of seal assembly 80 andthe pocket of the present invention will be determined by the size ofthe cylinders, and the resulting annular space, where said seal assembly80 is to be used.

Referring back to FIG. 2, unidirectional seal member 80 is disposed in apocket or seat within fluid channel 24 positioned between chamber 22 andchamber 23. Ring-like body member 81 is disposed around the outersurface of central mandrel 10, with surface 85 oriented generally in thedirection of first chamber 22, while substantially “Y”-shaped section,having substantially parallel finger members 83 and central vertexsection 84, is oriented generally in the direction of second chamber 23.

Said unidirectional seal member 80 allows fluid to flow from chamber 22into chamber 23. However, said seal member 80 forms a fluid pressureseal that prevents fluid flow in the opposite direction—that is, fromchamber 23 into chamber 22. As such, it is to be observed that any fluidthat flows from lower first chamber 22 into upper second chamber 23effectively becomes trapped within said chamber 23, and cannot flow in areverse direction past unidirectional seal member 80 back into saidlower first chamber 22.

The above-described invention has a number of particular features thatshould preferably be employed in combination, although each is usefulseparately without departure from the scope of the invention. While thepreferred embodiment of the present invention is shown and describedherein, it will be understood that the invention may be embodiedotherwise than herein specifically illustrated or described, and thatcertain changes in form and arrangement of parts and the specific mannerof practicing the invention may be made within the underlying idea orprinciples of the invention.

What is claimed:
 1. A down hole tool assembly for installation in awellbore comprising: a) a mandrel having a proximate end, a distal end,an outer surface and a central through bore; b) a lower body memberaffixed to said distal end of said mandrel, wherein said lower bodymember has a larger outer diameter than said mandrel; c) a settingcylinder having a central bore, wherein said mandrel is slidablydisposed within said central bore of said setting cylinder; d) a slipassembly disposed between said setting cylinder and lower body member;e) a seal assembly disposed between said setting cylinder and said bodymember; f) a first chamber formed between said mandrel and said settingcylinder; g) a second chamber formed between said mandrel and saidsetting cylinder, wherein said first and second chambers are in fluidcommunication with each other; and h) a unidirectional seal memberdisposed between said first and second chambers, wherein said sealmember permits fluid to flow from said first chamber to said secondchamber, but not from said second chamber to said first chamber.
 2. Thedown hole tool assembly of claim 1, wherein said slip assembly extendsradially outward to grip an inner surface of said wellbore.
 3. The downhole tool assembly of claim 1, wherein said slip assembly is locatedeither above or below said seal assembly.
 4. The down hole tool assemblyof claim 1, wherein said slip assembly comprises a plurality of slipmembers.
 5. The down hole tool assembly of claim 4, wherein said slipmembers can be oriented bi-directionally.
 6. The down hole tool assemblyof claim 1, wherein said seal assembly extends radially outward tocreate a fluid pressure seal against the inner surface of said wellbore.7. The down hole tool assembly of claim 1, further comprisingincompressible fluid in said first and second chambers.
 8. The down holetool assembly of claim 1, wherein axial movement of said settingcylinder toward said distal end of said mandrel creates a reduction involume of said first chamber and increases volume of second chamber. 9.The down hole tool assembly of claim 8, wherein said reduction in volumeof said first chamber forces incompressible fluid from said firstchamber to said second chamber.
 10. The down hole tool assembly of claim1, wherein said unidirectional seal allows said incompressible fluid toflow from said first chamber to said second chamber, but prevents saidincompressible fluid from flowing from said second chamber to said firstchamber.
 11. The down hole tool assembly of claim 1, wherein said sealassembly is constructed entirely of elastomeric material.
 12. The downhole tool assembly of claim wherein said lower body member furthercomprises a muleshoe.
 13. The down hole tool assembly of claim 1 furthercomprising a setting tool.
 14. The down hole tool assembly of claim 13,wherein said setting tool is adapted to apply force to said settingcylinder in a first axial direction and said central mandrel in anopposite axial direction.
 15. The down hole tool assembly of claim 14,wherein said setting tool can be selectively removed from a wellborefollowing anchoring of said down hole tool assembly in said wellbore.